1. Field of the Invention
The present invention relates to a method of manufacturing a toner.
2. Description of the Related Art
Along with remarkable development of office automation equipment in resent years, printers, facsimiles, copying machines that conduct printing by an electrophotographic method have been popularized. In electrophotographic methods, images are formed generally by utilizing photoconductive materials that form static images on the surface of a light sensitive body by various means, developing the static images with a toner and fixing the toner images on a transfer material such as paper.
The method of manufacturing toners for developing static images (hereinafter referred to as “static image developing toner”) have been generally classified so far into a dry method and a wet method. The dry method includes, for example, a pulverization method of kneading a binder resin, a colorant, etc., and pulverizing and classifying them. On the other hand, the wet method includes, for example, (i) a suspension polymerization method of polymerizing a monomer of a binder resin dispersed in an organic solvent by an organic suspension stabilizer under the presence of a colorant and incorporating the colorant in the resultant binder resin particles to obtain a toner, (ii) a coagulation method by emulsion polymerization of mixing a liquid resin dispersion and a liquid colorant dispersion formed by dispersing a colorant into an organic solvent to form coagulated particles and heating to fuse the coagulated particles to obtain a toner, (iii) a phase transition emulsion method of dissolving or dispersing a water dispersible resin and a colorant into an organic solvent, adding thereto a neutralizing agent that neutralizes dissociation groups of the water-soluble resin and water under stirring to form resin droplets incorporating the colorant, etc., and subjecting them to phase transition emulsification to obtain a toner, (iv) a method of dissolving or dispersing a binder resin and a colorant into an organic solvent to which the binder resin is soluble, mixing them with an aqueous dispersion of a less water-soluble alkaline earth metal salt such as calcium phosphate or calcium carbonate, conducting pelleting and removing the organic solvent to obtain a toner (for example, refer to Japanese Unexamined Patent Publication JP-A 7-152202 (1995), 7-168395 (1995), 7-168396 (1995), 7-219267 (1995), 8-179555 (1996), 8-179556 (1996), and 9-230624 (1997)), (v) an emulsifying dispersion method of dissolving or dispersing a binder resin and a colorant in a water insoluble organic solvent, dispersing under emulsification the solution or the liquid dispersion into an aqueous dispersion and then removing the organic solvent to obtain a toner (for example, refer to Japanese Unexamined Patent Publication JP-A 7-325429 (1995), 7-325430 (1995), 7-333890 (1995), 7-333899 (1995), 7-333901 (1995), and 7-333902 (1995)). Further, (f) a method of mixing a molten material of a resin having a ionic group and a colorant, and an aqueous medium containing a material that neutralizes the ionic groups under heating and pressure to obtain a toner is also known (for example, refer to the specification of Japanese examined Patent Publication JP-B 3351505).
Toners obtained by the dry method have particle size distribution of a relatively wide range and tend to vary in the charging performance. Formation of images by using a toner with such varied charging performance is not preferred since this generates color shading or the like in the images. On the contrary, since a toner with small grain size distribution and less variation of the charging performance can be produced relatively easily by the wet method, the wet method is often adopted in the manufacture of the toner. However, the wet method also involves a problem to be solved.
For example, an organic solvent for dissolving or dispersing the binder resin, a monomer for the binder resin, etc., sometimes remains slightly in the obtained toner particles to vary the charging performance of the toner particles. Further, the shape of the toner particles becomes uneven to vary the charging performance depending on the pressure (depressurization), temperature, time, etc. upon removing the organic solvent for solving or dispersing the binder resin.
Further, in the suspension polymerization method mentioned the above (i), the organic suspension stabilizer remains on the surface of the obtained toner particles to worsen the charging performance of the toner particles. Removal of the organic suspension stabilizer requires a complicate step to increase the manufacturing cost of the toner.
Further, the method mentioned the above (vi) involves a problem in that the formed toner particles are adhered to each other to cause growing. For preventing this, while it is necessary to precisely control various conditions such as a liquid temperature in the mixing system after mixing, such control is actually difficult extremely.
Further, since the organic solvent, the monomer for the binder resin, etc. generally used in the wet method give large burden on the environment, it requires a disposal equipment to increase the manufacturing cost.
On the other hand, the toner obtained by the existent methods as described above do not provide the picture quality of images by using the same (image density, absence or presence of white background fogging, etc.) formed on a transfer material and characteristics such as a transfer ratio to the transfer material together at high level.